As 190 nations meet for December 3-14 U.N. climate talks on the resort island of Bali, looking for ways to broaden a pact to slow down global warming, experts say mangroves are not getting the attention they deserve as a protective coastal barrier.

"Mangroves are a natural way to lessen the severity of the impact (of climate change) to coastal communities," said urban planning and climate change expert Enda Atmawidjaja.

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"They are natural sea barriers, and they are also much cheaper then building sea walls made of concrete."

Indonesia, a sprawling archipelago of 17,000 islands, is extremely vulnerable to a rise in sea levels, storm surges or more intense tropical storms linked to global warming.

The U.N. climate panel says seas could rise by 18 to 59 cms (7-23 inches) by 2100. More than 40 million of Indonesia's 220 million population live less than 10 meters above sea level.

Mangroves are trees and shrubs that grow along a saline strip along the coast, now and then swamped by tides. The thin roots provide a habitat for shrimps and small fish, break up waves and hold back silt and soil from that damage coral reefs.

Mangroves can keep rising seas at bay to a certain extent, giving communities more time to adjust. The trees can help people cope with heatwaves and help break up waves in the event of a tropical storm.

DEFORESTED

But decades of rampant development along Indonesia's 57,000 kms (35,000 miles) coastline have left nearly 70 percent of its 5 million hectares (12 million acres) of mangrove forests deforested or degraded, scientist Hiroyuki Hatori told Reuters.

"Indonesia is the world's number one country in terms of mangroves. Some statistics say that 25 percent of the world's mangrove exist in Indonesia," said Hatori. "However in many areas of Indonesia mangroves are fast receding."

Like in many parts of Indonesia, vast swathes of mangrove forest in "the neck of Bali," a strip of land that connects a tiny peninsula in the south to the main part of the island, were turned into shrimp ponds during a boom in the 1980s.

But the ponds were soon abandoned, leaving large areas barren. Scientists later discovered that violent waves were chipping away at the coast, sparking fears that lower part of the island could be cut off in a decade's time.

A government project sponsored by Japan's development arm set off in the early 1990s to restore the area's vast mangroves, filling about 1,000 hectares of land with nearly 20 types of mangrove.

It became the first big-scale restoration project in Indonesia, with a mangrove nursery supplying free saplings to 18 restoration projects across Indonesia.

Today, project head Sasmitohadi said Indonesia has made giant leaps in its effort to preserve mangrove forests, but the increasing demand for settlements in the world's fourth most populous nation is putting pressure on the mangrove forests.

"To be honest, human beings are the biggest threat to mangroves," Sasmitohadi said. Small-scale conversion into shrimp and fish ponds also continue to pose a threat to mangroves.

"Indonesia should step up its conservation efforts for the world's next generation," Hatori said. "There are only 18 million hectares of mangrove forests left in the world, once degraded, it would be difficult to recover."